1. Field of the Invention
The present invention relates to piezoelectric vibrators, and particularly, to a tuning-fork-type bimorph piezoelectric vibrator including two piezoelectric bodies having opposite polarization directions bonded together to define a tuning fork structure.
2. Description of the Related Art
In recent years, vibrating gyroscopes have been widely used as rotational angle detectors for car navigation and image stabilizers to prevent motion blur in digital still cameras and digital video cameras.
Examples of vibrators included in such vibrating gyroscopes include a tuning-fork-type bimorph piezoelectric vibrator illustrated in FIG. 7 (see, e.g., Japanese Unexamined Patent Application Publication No. 2000-258164).
The conventional tuning-fork-type bimorph piezoelectric vibrator 10 is formed by bonding first and second piezoelectric bodies having opposite polarization directions together to define a tuning fork structure. A driving electrode 28b including two separate portions is arranged on a first principal surface defined by a surface of the first piezoelectric bodies. An alternating voltage is applied to the driving electrode 28b and causes fundamental vibrations in which legs 12a and 12b at an end of the vibrator are opened and closed from side to side. Then, when a rotational angular velocity is externally applied, the Coriolis force causes the legs 12a and 12b to vibrate in a bending mode in directions that are opposite to each other and substantially perpendicular to the directions of the fundamental vibrations. Then, an electric charge generated in the first piezoelectric body by the bending vibrations of the legs 12a and 12b is extracted from detecting electrodes 30a and 30b on a second principal surface defined by a surface of the second piezoelectric body. The extracted electric charge is differential-amplified, and thus, a rotational angular velocity can be detected.
Here, a difference between a resonance frequency of a driving system and that of a detecting system is referred to as detuning frequency. As the detuning frequency decreases, detection sensitivity increases, but responsiveness decreases. Therefore, the detuning frequency is appropriately set such that a desired detection sensitivity can be achieved within a desired range of detection.
However, in a conventional tuning-fork-type bimorph piezoelectric vibrator, such as the tuning-fork-type bimorph piezoelectric vibrator described above, a detuning frequency changes significantly with temperature. This causes significant changes in the detection sensitivity and makes it difficult to accurately determine a rotational angular velocity.
Moreover, since the detuning frequency changes significantly with temperature, adjustment of the detuning frequency is time consuming and failure to adjust the detuning frequency may cause defects in the vibrator.
Additionally, since it is necessary to connect the detecting electrodes to external circuits, problems such as increased cost and variations in characteristics occur.